The present invention relates to a vehicle driveline clutch actuator which utilizes a ball ramp mechanism to load a clutch pack and more specifically to a vehicle driveline clutch actuator using a ball ramp mechanism having an intermediate plate interposed between a control plate and an activation plate to load a clutch pack where a pair of one-way clutches are used to provide continuous clutch engagement.
Driveline master clutches commonly use a plurality of springs to clamp a friction disc to an engine flywheel. The clamping springs are normally disposed within a pressure plate assembly which is bolted to the flywheel. The friction discs are splined to rotate with a transmission input shaft which when rotated, provides motive power to the driveline and wheels. A mechanical linkage operated by a driver is used to control the operation of the master clutch.
Efforts to automate the operation of the master clutch to take the place of the driver are currently underway. It is known to make use of a hydraulic actuator or an electric motor to operate the master clutch release mechanism in response to a control signal generated by a control microprocessor in response to a multiplicity of sensor outputs which are used to determine the vehicle operating conditions and hence the desired operation of the master clutch.
The use of a ball ramp actuator to operate a driveline master clutch is known in the art. U.S. Pat. Nos. 5,441,137; 5,469,948; 5,505,285; 5,651,437; 5,810,141; 5,910,061; 5,964,330; and RE 36,502 assigned to the same assignee as this application, all of which are hereby expressly incorporated by reference, disclose methods of using a ball ramp actuator to supply the clamping force on a clutch disc which can be used to frictionally rotationally connect the engine flywheel to the transmission input shaft. The ball ramp actuator is activated when a electrical current is supplied to a coil thereby producing an electromagnetic field in a coil pole which applies a retarding force to a rotating armature. The rotating armature is commonly nonrotatably connected to an annular control plate which has a plurality of control ramps which vary in depth. An opposed annular activation plate has a like number of opposed variable depth activation ramps where a corresponding number of rolling elements are trapped between the control and activation ramps. As the retarding force is applied to the control plate, the rotational movement of the control plate relative to the activation plate causes the rolling elements to traverse the control ramps and the activation ramps thereby causing an increase in separation distance between the control and activation plates to provide the clutch disc clamping force.
Also shown in the prior art are other types of vehicle driveline devices which make use of a ball ramp mechanism to provide a clamping load to a clutch pack. U.S. Pat No. 5,092,825 discloses a limited slip differential having a clutch pack loaded by a ball ramp actuator. U.S. Pat. No. 5,499,951 discloses a driveline transfer case where the torque split is controlled by a ball ramp actuator. U.S. Pat. No. 5,528,950 discloses a transmission inertia brake where a ball ramp actuator loads a clutch pack to slow a spinning transmission shaft. U. S. Pat. No. 5,819,883 discloses a driveline retarder in which a ball ramp actuator is used to load a clutch pack to rotate a hydraulic pump in response to a signal from a control unit. The disclosures of U.S. Pat. Nos. 5,092,825; 5,499,951; 5,528,950 and 5,819,883 are all hereby incorporated by reference.
In the prior art, operation of the master clutch or other driveline coupling system such as a differential or transfer case could be improved by improving the inherent mechanical stability of the ball ramp. It would also be an advantage if the clutch remained fully engaged irregardless of the direction of the flow of torque through the clutch while using a ball ramp mechanism with unidirectional ramps in the control and activation plates.
The present invention results in an improvement in the operational characteristics of a ball ramp actuator which can be used in a variety of vehicle driveline applications to supply a clamping load to a frictional clutch pack. The present invention provides a unidirectional apply ball ramp function along with significantly increased frictional damping in the ball ramp mechanism to control and stabilize the ball ramp mechanism and thereby improve the operation of the master clutch or other driveline device.
One-way clutches are used to control the rotational direction of the coil armature and the rotational direction of the activation plate to provide a continuous clutch apply function using unilateral grooves in the control plate and activation plate where the clutch clamping load is maintained irregardless of the direction of torque flow in the clutch assembly. The operating direction of the one-way clutches are oriented in opposite directions.
To improve the operation of the ball ramp mechanism, the stability is improved by significantly increasing the frictional damping using an intermediate plate disposed between the activation plate and the control plate where the intermediate plate rotates with the input shaft and hub. Note that the torque flow from the input shaft to the output shaft can be reversed so that the torque flows from the output shaft to the input shaft. The coil assembly generates an electromagnetic force that frictionally rotationally couples the coil armature, the control plate, the intermediate plate and the activation plate together. The one-way clutches are oriented to only allow the coil armature to rotate in an opposite direction from that of the activation plate. The activation plate rotates on a first one-way clutch on the output shaft while the intermediate plate is driven by the hub and the coil pole rotates on a second one-way clutch also on the output shaft.
One provision of the present invention is to provide a ball ramp actuator to load a clutch pack.
Another provision of the present invention is to provide a ball ramp actuator to load a clutch pack where the clutch clamp load is maintained irregardless of the direction of driveline torque flow.
Another provision of the present invention is to provide a ball ramp actuator to load a clutch pack where the frictional damping of the ball ramp control system is substantially increased to improve operation.
Still another provision of the present invention is to provide a ball ramp actuator to load a driveline master clutch disc having improved operational characteristics.